Abscisic acid is a plant hormone that involves in plant responses to various environmental stresses. For example, when a plant is suffered from dry stress, abscisic acid is rapidly accumulated, and then, pore closing and expression of stress-related genes such as rab18, kin1, and rd29B are promoted. As for abscisic acid biosynthesis in plants, a major pathway involves, via a carotenoid of a compound comprising 40 carbon atoms, use of xanthoxin having 15 carbon atoms as a precursor, which is generated by the degradation of the carotenoid, and oxidation of the hydroxyl group at the 3′-position, the isomerization of the double bond derived from the epoxy cleavage; and the oxidation of the aldehyde into carboxylic acid. In particular, the cleavage reaction of epoxycarotenoid by dioxygenase [nine-cis-epoxycarotenoid dioxygenase (NCED)] into xanthoxin is considered as a reaction that controls the abscisic acid biosynthesis.
In order to elucidate physiological functions of abscisic acid, which is a plant hormone essential for plant growth, methods has been used so far wherein abscisic acid is directly applied to a plant, or wherein a mutant whose gene for the abscisic acid biosynthesis is destroyed is used to analyze expressed physiological phenomena. However, by the application of abscisic acid, which already exists in the plant body, it is difficult to elucidate actual physiological actions of inherent abscisic acid. The methods using the mutants, which are in deficient stage of abscisic acid, are useful for investigation of the functions of abscisic acid by comparison with wild strains in physiological phenomena and morphologic states. However, the methods have disadvantages in that they are inapplicable to various plants and the abscisic acid deficient state cannot be controlled in a desired growth period.
As a method for compensating the disadvantages of the methods available to date, inhibitors against the abscisic acid biosynthesis can be utilized. In order to artificially obtain an abscisic acid deficient plant, agents inhibiting the biosynthesis of carotenoid, which is an intermediate of the abscisic acid biosynthesis, have already been used; however, such agents have potent whitening action, and accordingly, they are inappropriate for investigation of an abscisic acid deficient state without involvement of side effects. Under these circumstances, if a specific inhibitor against abscisic acid can be provided, various plants can easily be introduced in an abscisic acid deficient state, and analytical studies of abscisic acid functions can be expectedly progressed. In addition, an abscisic acid biosynthesis inhibitor can be utilized as a plant growth regulator which is effective for various growth processes of plants. It has been reported that NDGA [4,4′-(2,3-dimethyl-1,4-butanediyl)bis-1,2-benzenediol] which is known as a peroxidase inhibitor has inhibitory action on the abscisic acid biosynthesis on the basis of the results of inhibitory test of pore closing activity and the analysis of the amount of inherent abscisic acid production (Plant Physiology (1992) 99, 1258–1260).